1. Field of the Invention
This invention relates to a toner empty detecting system for use in an electrophotographic printer or the like.
2. Description of the Related Art
In a conventional electrophotographic printer, when the residual quantity of a toner becomes less than a predetermined amount (this condition will hereinafter be referred to as "toner-empty condition"), the quality of the print copies deteriorates. Therefore, generally such a printer is provided with means for detecting the toner-empty condition. In order to ensure a satisfactory printing quality, the detection of the toner-empty condition must be performed correctly.
A conventional toner empty detecting system of an electrophotographic printer will now be described with reference to a block diagram of FIG. 3 (prior art) and a flow chart of FIG. 4 (prior art). During printing, a controller 1 monitors the output of a toner sensor 3 mounted within a developing machine 2 at predetermined time intervals T. When a toner-empty signal is detected (Step 401), the controller 1 increments a counter 4 (Step 402) and when a toner-present signal is detected, the controller 1 clears the counter 4 (Step 403). The controller 1 repeats this operation of incrementing and clearing the counter 4 until the count of the counter 4 is able to reach a certain value N1 (Step 404) because no toner-present signals were detected during a given time period. Then, the controller judges that the toner-empty condition exists, stops the printing (Step 405), and instructs a display device 5 to display the toner-empty condition (Step 406).
Typically, the fluidity of the toner is deteriorated by moisture or the like so that the toner in the developing machine 2 may decrease unevenly. In such a case, only the toner on the surface of the toner sensor 3 deteriorates, therefore, the toner sensor may erroneously detect the toner-empty condition.
When the toner-empty condition is detected even though the toner still remains, the operator generally does not realize that toner still remains, and therefore feeds a fresh supply of toner in accordance with the toner-empty message. As a result, the added toner may exceed the capacity as allowed for by the developing machine 2 and overflow.